This invention relates generally to the field of disc drive data storage devices and more particularly, but without limitation, to performing real-time, closed loop write verification by detecting electromagnetic coupling of constituent components making up the write path in the disc drive.
Modern data storage devices such as disc drives are commonly used in a multitude of computer environments to store large amounts of data in a form that is readily available to a user. Generally, a disc drive has a magnetic disc, or two or more stacked magnetic discs, that are rotated by a motor at high speeds. Each disc has a data storage surface divided into a series of generally concentric data tracks where data is stored in the form of magnetic flux transitions.
A data transfer member (sometimes referred to as a read/write head) such as a magnetic transducer is moved by an actuator to selected positions adjacent the data storage surface to sense the magnetic flux transitions in reading data from the disc, and to transmit electrical signals to induce the magnetic flux transitions in writing data to the disc. The active elements of the data transfer member are supported by suspension structures extending from the actuator. The active elements are maintained a small distance above the data storage surface as the data transfer member flies upon an air bearing generated by air currents caused by the spinning discs.
Each read/write head is typically provided with separate read and write elements, with a common configuration utilizing a thin film, inductive write element and a magneto-resistive (MR) read element. Data are written by passing a write current through the write element, with the write current generating a time-varying electromagnetic field which accordingly magnetizes the disc surface. Previously written data are read using the read element to transduce the selective magnetization of the disc to generate a read signal which is received by a read channel to reconstruct the data. An interface circuit buffers and controls the transfer of data between the disc and a host computer.
Technological advancements in the art have resulted in continued improvements in disc drive data storage capacities and transfer rates, as well as the reliability with which the data is stored and recalled. Design cycle times are continually being accelerated as well, with each new generation typically providing a doubling in storage capacity. These fast-paced advancements have driven the need for improved methodologies that ensure that data is consistently and accurately stored and retrieved.
One such methodology to ensure data integrity involves the grouping of a plurality of disc drives into a multi-drive array, sometimes referred to as a RAID (xe2x80x9cRedundant Array of Inexpensive Discsxe2x80x9d). Since their introduction, RAIDs have found widespread use in a variety of applications requiring significant levels of data transfer, capacity and integrity performance. One such RAID architecture employs mirroring, where data is simultaneously written to two or more disc drives. Another approach employs striping, where portions of data streams are written to different disc drives. Yet another approach employs interleaving wherein various types of error detection and correction schemes are carried out at multiple levels.
Another popular methodology useful in ensuring data integrity is write verification, which involves the writing of data to a disc followed by a subsequent read operation where the previously stored data are retrieved from the disc to ensure the data were correctly written. However, such write verification operations undesirably decrease the data transfer performance of the disc drive, as each write operation requires each sector to which data are written to be accessed at least twice: first, when the data are written, and second, when the data are subsequently read back for verification. Conventional write verification techniques accordingly impose a severe penalty on disc drive performance, limiting data transfer rates to levels substantially below that which would be otherwise achievable.
Yet another methodology involves real-time monitoring of the write head during a write operation. Writing failures can stem from a defective write element; that is, a write element that is electrically open or shorted. During data writing operations there exists an observable expected amount of electromagnetic coupling within the constituent parts of the electrical read/write path. It has been determined that an optimal solution for ensuring a write-safe condition of the write element lies in simultaneously verifying the expected electromagnetic coupling effects while writing data. It is to these improvements and others as exemplified by the description and appended claims that embodiments of the present invention are directed.
The embodiments of the present invention contemplate a disc drive comprising a rotatable disc having a magnetic recording surface, and a data reading and writing assembly. The data reading and writing assembly comprises a read/write head comprising a write element and a read element, both adjacent the recording surface; a preamplifier comprising a write driver applying a series of write currents for writing data to the recording surface and a read amplifier for reading stored data from the recording surface; and an interconnect joining the write driver to the write element so as to generate time-varying electromagnetic fields selectively magnetizing the recording surface in response to the write currents, and joining the read amplifier to the read element so as to transduce magnetization vectors on the recording surface associated with stored data. The disc drive furthermore comprises a detection circuit connected to the data reading and writing assembly, receiving a write-safe signal indicative of a write-safe condition, the write-safe signal comprising a sum of constituent operable electromagnetic coupling values of the read/write head, the preamplifier and the interconnect.
In one embodiment the detection circuit is connected to the preamplifier and receives the write-safe signal when a bias current is directed to the read element while writing data to the recording surface, such that a reversal in the writing current generates an electromagnetic coupling effect in the bias current. An advantageous construction comprises adaptively connecting the circuit to the analog buffer head voltage terminal of the preamplifier.
Embodiments of the present invention further contemplate a method for writing data in a data storage device, comprising: (a) generating a write current signal associated with the data to be written with a write driver portion of a preamplifier; (b) transmitting the write current signal along an interconnect to a magneto resistive write element portion of a read/write head to generate a time-varying electromagnetic field imparting flux transitions associated with the data in a data storage portion of the data storage device; (c) supplying a bias current to a read portion of the read/write head; (d) while transmitting the write current, simultaneously reading an electromagnetic coupling signal comprising constituent coupling signals of the preamplifier, the interconnect and the read/write head; and (e) comparing the electromagnetic coupling signal to a threshold value indicative of a write-safe condition of the write element.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.